p-Aminobenzamidine is, like benzamidine, a competitive inhibitor of the serine proteases trypsin (1), plasmin and thrombin (2), but it is more active than benzamidine. The active concentration ranges from 1 mM (3, 4) to 2 mM (5). For the preparation of plant cell extracts, a working concentration of 1 mM is recommended (100X stock solution 0.1 M in water; ref. 4).